554 



Comparative Animal Physiology 



trasystoles led Hoff**^ to the conclusion that the QRST complex represents 

 the algebraic summation of impulses arriving asynchronously at the different 

 surfaces of the heart. The T wave is said to represent repolarization of the 

 ventricular surface, an upright T indicating earlier repolarization of the left 

 ventricle, an inverted T earlier repolarization of the right side of the heart 

 (Figs. 199, 200).^^ That the T wave represents repolarization is indicated 

 by the action potentials of strips of heart muscle. ^° 



V 



V 

 -A. 



J-J. 



1 I 1 i 1 i 1 i i I i I ,M M t 



Pig. 200. Electrocardiogram from an eel. A, Normal ECG. B, Activity of 

 isolated sinus venosus. From Bakker." 



Fig. 201. Electrocardiogram of systemic heart of Octopus. From Luisada.^^* 



The potentials of eel lymph hearts may be separated into two phases, a 

 fast and a slow component.'"' Transplanted lymph hearts of the frog yield 

 a simple diphasic wave. '"•^ 



The electrocardiogram of other myogenic hearts also consists of slow 

 electrical waves. The chambered hearts of Octopus (Fig. 201) show an in- 

 itial fast deflection, followed by a prolonged wave of negativity. '■*-• '-^ In 

 Aplysia the ECG consists of slow waves with irregular deflections superim- 

 posed."^ In Helix the waves are nearly smoflth and consist of fast systolic 



